VLBI, MERLIN and HST observations of the giant radio galaxy 3C 236

We present VLBI and MERLIN data at 1.66 and 4.99 GHz on the central compone nt coincident with the nucleus of the giant radio galaxy, 3C 236. The nucle ar radio structure is composed of two complexes of emission which are resol ved on scales from 1 milli-arcsec (mas) to 1 arcsec. Oscillations with an a mplitude of similar to5 degrees can be seen in the compact radio structure. Spectral index distributions are plotted at angular resolutions of 10 and 25 mas and allow us to identify the core component in the south-east emissi on complex. Re-examination of the HST WFPC-2 image of 3C 236 by de Koff et al. (2000), shows that the normal to the dust disk in the nucleus is simila r to 30 degrees from the plane of the sky and within 12 degrees of parallel to the overall orientation of the radio source. We suggest that the radio axis is also at an angle of similar to 30 degrees to the plane of the sky a nd that the north-west jet is on the approaching side. This orientation imp lies an overall size of 4.5 Mpc (H-0 = 75 kms(-1) Mpc(-1), q(0) = 0.5) for 3C 236. The coincidence of a dust feature and the south-east compact jet, w ithin the astrometric errors, leads us to suggest that the dust may be in t he form of a cloud encountered by the jet in the first similar to 400 pc of its journey out from the nucleus. One-sided emission at 5 GHz on 1 mas sca les would suggest that the jets are ejected initially at less than or equal to 35 degrees to the line of sight, but this is difficult to reconcile wit h the obvious orientation stability of the jet system as a whole. Free-free absorption of the counter-jet may be an alternative explanation for the on e-sideness. At the resolution of WSRT data at 327 MHz, the jet to the south -east is apparently continuous over a distance of 2.5 Mpc, making this the largest jet known in the universe. It is likely, however, that activity in the nucleus of 3C 236 is episodic but with a shorter duty cycle than in the double-double sources studied by Schoenmakers et al. (2000) and Kaiser et al. (2000).